This work reports the systematic electrical transport measurements of layered dichalcogenide $2H-\mathrm{NbS}{\mathrm{e}}_2$ by indium (In) doping forming the ${\left(\mathrm{InS}{\mathrm{e}}_2\right)}_x\mathrm{NbS}{\mathrm{e}}_2$. The results of resistivity and magnetization indicate that the onset superconducting transition temperature is about 10.31 K and the out-of-plane upper critical field ${\mu }_0{H}_{c2\perp }\left(0\right)=11.81$ T, which are both significantly enhanced when compared with undoped $\mathrm{NbS}{\mathrm{e}}_2$. The phase diagram obtained by anisotropic magnetoresistance measurements shows that both superconducting and normal states of ${\left(\mathrm{InS}{\mathrm{e}}_2\right)}_x\mathrm{NbS}{\mathrm{e}}_2$ are isotropic, except for a weak twofold symmetry in the low-temperature high-field region. Such behavior is strikingly different from previously known layered superconductors and indicates a three-dimensional electronic structure in ${\left(\mathrm{InS}{\mathrm{e}}_2\right)}_x\mathrm{NbS}{\mathrm{e}}_2$. The Hall measurements suggest that the electron-type carrier is dominant in ${\left(\mathrm{InS}{\mathrm{e}}_2\right)}_x\mathrm{NbS}{\mathrm{e}}_2$ with relatively low carrier concentration, and the calculations of $k_{\mathrm{F}}\xi , {\mathrm{\Delta }}_0/E_{\mathrm{F}}$, and $T_c/T_{\mathrm{F}}$ suggest the potential for ${\left(\mathrm{InS}{\mathrm{e}}_2\right)}_x\mathrm{NbS}{\mathrm{e}}_2$ in exploring the superconductivity in the BCS-BEC crossover regime.

Recently, two-dimensional ${\mathrm{Nb}}_2\mathrm{C}$ has garnered increasing attention, both experimentally and theoretically, due to its functional-group-dependent superconductivity. In contrast to the halogen and chalcogen additives that were the main focus of previous studies, we study the effect of lithium adsorption, which can also be incorporated during the synthesis of ${\mathrm{Nb}}_2\mathrm{C}$. Our computational analysis reveals a metal-to-superconductor transition in monolayer ${\mathrm{Nb}}_2\mathrm{C}$ with a critical temperature $T_{\mathrm{c}}$ of 22.1 K and a strong anisotropic superconducting gap distribution following the adsorption of lithium atoms. This emergent superconductivity is attributed to the increased number of electronic states at the Fermi energy, resulting from the contribution of Nb $d$ orbitals and electron gas states induced by the low electronegativity of lithium. Furthermore, the application of tensile strain raises the $T_{\mathrm{c}}$ to 24 K, which is higher than that of most functional-group-modified ${\mathrm{Nb}}_2\mathrm{C}$ systems. Our work deepens the understanding of electron-phonon coupling in layered ${\mathrm{Nb}}_2\mathrm{C}$ and provides insights into achieving high critical temperature superconductivity with a strong anisotropic superconducting gap distribution in this system.

In the nonadiabatic dynamics across a quantum phase transition, the Kibble-Zurek paradigm describes that the average number of topological defects is suppressed as a universal power law with the quench time scale. A conflicting observation, termed anti-Kibble-Zurek dynamics, has been reported in several studies, specifically in the driven systems with an uncorrelated stochastic (white) noise. Here, we study the defect generation in the driven transverse field/anisotropy quantum XY model in the presence of a correlated (colored) Gaussian noise. We propose a generic conjecture that properly captures the noise-induced excitation features, which shows good agreement with the numerical simulations. We show that the dynamical features of defect density are modified by varying the noise correlation time. Our numerical simulations confirm that, for fast noises, the dynamics of the defect density is the same as that of the uncorrelated (white) noise, as is expected. However, the larger ratio of noise correlation time to the annealing time results in larger defect density formation and reforms the universal dynamical features. Our finding reveals that the noise-induced defects scale linearly with the annealing time for fast noises, while in the presence of slow noises the noise-induced defects scale linearly with the square of the annealing time. The numerical simulations confirm that the optimal annealing time, at which the defect density is minimum, scales linearly in logarithmic scale with the total noise power having different exponents for fast and slow noises.

The entanglement of electronic spin and orbital degrees of freedom is often the precursor to emergent behaviors in condensed matter systems. With considerable spin-orbit coupling strength, the cobalt atom on a honeycomb lattice offers a platform that can make accessible the study of novel magnetic ground states. Using temperature-dependent Raman spectroscopy and high-magnetic-field Raman and IR spectroscopy, we studied the lattice and spin-orbital excitations in ${\mathrm{CoTiO}}_3$, an antiferromagnetic material that exhibits topologically protected magnon Dirac crossings in the Brillouin zone. Under the application of an external magnetic field up to 22 T along the crystalline $c$ axis, we observed the splitting of both the spin-orbital excitations and a phonon nearby in energy. Using density functional theory (DFT), we identify a number of modes that below the antiferromagnetic (AFM) transition become Raman active due to the zone folding of the Brillouin zone caused by the doubling of the magnetic unit cell. The phonon splitting under an applied magnetic field, or the phonon Zeeman effect, is observed in both a zone-centered phonon as well as its zone-folded counterpart. We use a model that includes both the spin and orbital degrees of freedom of the $\mathrm{Co}{}^{2+}$ ions to explain the spin-orbital excitation energies and their behavior in an applied field. Our experimental observations along with several deviations from the model behavior point to significant coupling between the spin-orbital and the lattice excitations.

In this paper, we explore the magnetic behavior of diluted spin-ice systems, where magnetic moments are randomly removed at various concentrations. We concentrate on features in which the effect of long-range dipolar interactions (usually masked by self-screening in these systems) is made visible by dilution. Our initial focus is on the configurations reached after cooling to low temperatures at zero field, sweeping the whole density range of impurities. We observe that the missing magnetic moments induce a certain type of local, magnetic charge order. Next, using Monte Carlo simulations, we examine the behavior of the magnetization under an applied magnetic field in the [111] crystallographic direction. The inclusion of dipolar interactions allows us to account for the main features observed in previous experimental results. Using the dumbbell model, where magnetic moments are represented as pairs of oppositely charged magnetic monopoles, we can understand the qualitative behavior of these curves as we increase doping. Additionally, we use this framework to calculate the critical fields corresponding to the phase transition observed in pure samples and the characteristic fields appearing at very low doping.

We utilize the fluctuation-exchange approximation on a bilayer two-orbital model, incorporating $d_{x^2-y^2}$ and $d_{z^2}$ orbitals, to explore potential pairing symmetries in the bilayer nickelate ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$. Our study particularly examines the impact of interlayer Coulomb interactions. In the absence of these interactions, the superconducting gap exhibits $s_{\pm }$-wave symmetry, with predominant intraorbital pairing in the $d_{z^2}$ orbital. As interlayer interactions increase, $s_{\pm }$-wave superconductivity is suppressed, while the superconductivity with a $d_{x^2-y^2}$-wave gap is enhanced, resulting in a transition at a critical interaction strength. This $d_{x^2-y^2}$-wave superconductivity is distinct not only from the $s_{\pm }$-wave superconductivity but also from the intraorbital $d$-wave pairing in cuprate superconductors, as it is dominated by the interlayer pairing between the $d_{x^2-y^2}$ and $d_{z^2}$ orbitals. Additionally, charge fluctuations play a crucial role in driving the transition from $s_{\pm }$-wave to $d_{x^2-y^2}$-wave superconductivity. Our findings indicate that interlayer Coulomb interactions are crucial for understanding the pairing mechanism in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$.

We report on studies of the superconducting and normal-state properties of the noncentrosymmetric superconductor BeAu under hydrostatic pressure conditions. The room-temperature equation of state (EOS) reveals the values of the bulk modulus ($B_0$) and its first derivative ($B_0^{\prime }$) at ambient pressure to be $B_0\simeq 133\mathrm{GPa}$ and $B_0^{\prime }\simeq 30$, respectively. Up to the highest pressures studied ($p\simeq 2.2\mathrm{GPa}$), BeAu remains a multigap type-I superconductor. The analysis of $B_{\mathrm{c}}(T,p)$ data within the self-consistent two-gap approach suggests the presence of two superconducting energy gaps, with the gap-to-$T_{\mathrm{c}}$ ratios ${\mathrm{\Delta }}_1/k_{\mathrm{B}}{T}_{\mathrm{c}}\sim 2.3$ and ${\mathrm{\Delta }}_2/k_{\mathrm{B}}{T}_{\mathrm{c}}\sim 1.1$ for the larger and smaller gaps, respectively [$\mathrm{\Delta }=\mathrm{\Delta }\left(0\right)$ is the zero-temperature value of the gap and $k_{\mathrm{B}}$ is the Boltzmann constant]. With increasing pressure, ${\mathrm{\Delta }}_1/k_{\mathrm{B}}{T}_{\mathrm{c}}$ increases while ${\mathrm{\Delta }}_2/k_{\mathrm{B}}{T}_{\mathrm{c}}$ decreases, suggesting that pressure enhances (weakens) the coupling strength between the superconducting carriers within the bands where the larger (smaller) superconducting energy gap has opened. The superconducting transition temperature $T_{\mathrm{c}}$, the zero-temperature values of the superconducting gaps ${\mathrm{\Delta }}_1$ and ${\mathrm{\Delta }}_2$, and the zero-temperature value of the thermodynamic critical field $B_{\mathrm{c}}\left(0\right)$ decrease with increasing pressure, with the rates of $\mathrm{d}{T}_{\mathrm{c}}/\mathrm{d}p\simeq -0.197\mathrm{K}/\mathrm{GPa}, \mathrm{d}{\mathrm{\Delta }}_1/\mathrm{d}p\simeq -0.034\mathrm{meV}/\mathrm{GPa}, \mathrm{d}{\mathrm{\Delta }}_2/\mathrm{d}p\simeq -0.029\mathrm{meV}/\mathrm{GPa}$, and $\mathrm{d}{B}_{\mathrm{c}}\left(0\right)/\mathrm{d}p\simeq -2.65\mathrm{mT}/\mathrm{GPa}$, respectively. The measured $B_{\mathrm{c}}\left(0\right)$ values plotted as a function of $T_{\mathrm{c}}$ follow an empirical scaling relation established for conventional type-I superconductors.

Vortices in type-II superconductors driven over random disorder are known to exhibit a remarkable variety of distinct nonequilibrium dynamical phases that arise owing to the competition between vortex-vortex interactions, the quenched disorder, and the drive. These include pinned states, elastic flows, plastic or disordered flows, and dynamically reordered moving crystal or moving smectic states. The plastic flow phases can be particularly difficult to characterize since the flows are strongly disordered. Here, we perform principal component analysis (PCA) on the positions and velocities of vortex matter moving over random disorder for different disorder strengths and drives. We find that PCA can distinguish the known dynamic phases as well as or better than previous measures based on transport signatures or topological defect densities. In addition, PCA recognizes distinct plastic flow regimes, a slowly changing channel flow and a moving amorphous fluid flow, that do not produce distinct signatures in the standard measurements. Our results suggest that this position and velocity-based PCA approach could be used to characterize dynamic phases in a broader class of systems that exhibit depinning and nonequilibrium phase transitions.

The antiferromagnetic (AFM) order inside the superconducting (SC) phase of $\mathrm{CeCo}{\left({\mathrm{In}}_{1-x}{\mathrm{Zn}}_x\right)}_5$ ($x\le 0.06$) is investigated by neutron scattering, specific heat, and ac magnetic susceptibility measurements. It is confirmed that the AFM order with a modulation vector of $q_0=(1/2,1/2,1/2)$ develops for $x>0.03$, accompanied by the reduction of the SC transition temperature $T_c$ from 2.3 K ($x=0$) to 1.6 K ($x=0.06$). The AFM transition temperature $T_N$ and the staggered moment $\mu$ continuously increase from zero within the SC phase as $x$ increases beyond 0.03. For the small $x$ range satisfying the $T_N<T_c$ condition, the AFM Bragg peak intensity shows an unusually gradual development with a ${(T_N-T)}^2$ function below $T_N$ and the specific heat shows no anomaly at $T_N$. In contrast, when $T_N$ is larger than $T_c$ at $x=0.06$, the AFM Bragg peak evolves with the conventional $(T_N-T)$ dependence and a clear jump in the specific heat occurs at $T_N$. A coupling between the SC and AFM orders at the microscopic level is suggested to yield these unusual features observed in the small $x$ range.

Staggered magnetic fluxes (SMFs) play a crucial role in achieving Chern insulators (CIs), by which a series of CI models have been established on various lattices. In addition, a SMF induced higher-order topological insulator (HOTI) in a lattice model has been reported. In this work, we propose a square lattice model with SMF. We find intracellular SMF can induce a zero-Chern-number topological insulator at quarter filling which hosts topologically protected edge states characterized by the quantized polarization, in analogy to the topological state in a two dimensional Su-Schrieffer-Heeger model. When lattice dimerization and intracellular SMF are introduced, there exists a HOTI state at half filling. Furthermore, this model hosts a topological flat band (TFB) by considering the next-nearest-neighbor hoppings. Several fractional Chern insulator states are investigated when hard-core bosons are filled into this TFB model.

Topological orders in ($2+1$) dimensions are spontaneous symmetry-breaking (SSB) phases of 1-form symmetries in pure states. The notion of symmetry is further enriched in the context of mixed states, where a symmetry can be either “strong” or “weak.” In this work, we apply a Rényi-2 version of the proposed equivalence relation by [S. Sang et al. (unpublished)] on density matrices that is slightly finer than two-way channel connectivity. This equivalence relation distinguishes general 1-form strong-to-weak SSB (SW-SSB) states from phases containing pure states, and therefore labels SW-SSB states as “intrinsically mixed.” According to our equivalence relation, two states are equivalent if and only if they are connected to each other by finite Lindbladian evolution that maintains analytically varying, finite Rényi-2 Markov length. We then examine a natural setting for finding such density matrices: disordered ensembles. Specifically, we study the toric code with various types of disorders and show that in each case, the ensemble of ground states corresponding to different disorder realizations forms a density matrix with different strong and weak SSB patterns of 1-form symmetries, including SW-SSB. Furthermore, we show by perturbative calculations that these disordered ensembles form stable “phases” in the sense that they exist over a finite parameter range, according to our equivalence relation.

A recursive extension of the hybrid tetrahedron method for Brillouin-zone integration is proposed, allowing iterative tetrahedron refinement and significantly reducing the error from the linear tetrahedron method. The Brillouin-zone integral is expressed as a weighted sum on the initial grid, with integral weights collected recursively from the finest grid. Our method is capable of simultaneously handling multiple singularities in the integrand and thus may provide practical solutions to various Brillouin-zone integral tasks encountered in realistic calculations, including the computation of response and spectral function with superior sampling convergence. We demonstrate its effectiveness through numerical calculations of the density response functions of two model Hamiltonians and one real material system, the face-centered cubic cobalt.

The $f$-electron materials display many anomalous properties under pressure, making them of great interest in high-pressure physics and related industrial fields. However, the $f$-electrons pose a substantial challenge to simulations since the electron correlation effects. In this work, we present a first-principles calculation scheme for the equations of state (EoS) of $f$-electron materials. The self-consistent pressure-dependent on-site Coulomb correction is performed based on our recently developed doubly screened Coulomb correction approach. We investigated pressure dependence of the on-site Coulomb interaction, zero-temperature EoS over a wide range of pressures and the phase stabilities of four prototypical lanthanide and actinide metals, Pr, Eu, Th, and U. The simulated compressive properties agree better with the experimental data than those obtained by conventional density functional theory (DFT) and fixed-parameter $\mathrm{DFT}+U$ approaches. The pressure-induced phase transitions can also be well described.

We present magneto-optical studies of a self-assembled semiconductor quantum dot in neutral and positively charged states. The diamagnetic shifts and Zeeman splitting of many well-identified optical transitions are precisely measured. Remarkably, a pronounced negative diamagnetic shift is observed for spectral lines resulting from a doubly positively charged excitonic complex. We use the Hartree-Fock approximation for describing the direct Coulomb and exchange interactions between the quantum dot confined carriers in various configurations. A simple harmonic potential model, which we extend to capture the influence of an externally applied magnetic field in Faraday configuration, is then used to quantitatively account for all the measured diamagnetic shifts. We show that the negative shift is due to the change in the hole-hole exchange interaction energy induced by the magnetic field. Using this model and the measured shifts we extract the dielectric constant of the quantum dot material and get a decent estimate of the quantum dot dimensions. Further, the measured Zeeman splitting of the various spectral lines are also explained by a simple model using algebraic sums and differences of the $g$ factors of the confined charge carriers in their respective first and second discrete energy levels. Finally, the obtained values of the electronic $g$ factor and that of the dielectric constant are independently used to determine the effective composition $\left(x\right)$ of the ternary ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum dot. Both agree to within the experimental uncertainties.